Method and device for detecting cracks in semiconductor substrates

Abstract

A method and an apparatus for detecting cracks in semiconductor substrates, such as silicon wafers and solar cells, are provided. The method and apparatus are based on the detection of light deflected at a crack.

The invention claimed is: 
     
       1. A method for detecting cracks in planar, polycrystalline semiconductor substrates that have two opposite faces and a circumferential edge surface, comprising:
 directing electromagnetic radiation into the edge surface of the polycrystalline semiconductor substrate, the electromagnetic radiation having a wavelength that is at least partially transmitted by the polycrystalline semiconductor substrate so that the electromagnetic radiation is directed from the edge surface for at least half a distance to a point opposite the edge surface by reflection at the two opposite faces; 
 detecting electromagnetic radiation of at least a portion of one of the two opposite faces with an imaging optical detector that is sensitive to the electromagnetic radiation at the wavelength, wherein the electromagnetic radiation is scattered by the cracks and exits from one of the two opposite faces at sites of the cracks; 
 generating an image of scattering intensity from the electromagnetic radiation detected by the imaging optical detector; and 
 placing an opaque structure between the face of the polycrystalline semiconductor substrate and the imaging optical detector and recognizing a gleaming periphery of the opaque structure as a crack. 
 
     
     
       2. The method according to  claim 1 , further comprising moving the polycrystalline semiconductor substrate and the light source relative to each other in an advance direction along the two opposite faces and transversely to a direction of incidence of the electromagnetic radiation while directing the electromagnetic radiation into the edge surface by the laser such that a point of incidence of the light beam is moved along the edge surface of the polycrystalline semiconductor substrate,
 wherein the image of scattering intensity is generated from the electromagnetic radiation detected by the imaging optical detector during the relative movement. 
 
     
     
       3. The method according to  claim 1 , wherein the electromagnetic radiation comprises infrared light having a wavelength of at least 1.2 micrometers. 
     
     
       4. The method according to  claim 1 , further comprising detecting the cracks by evaluating a local brightness distribution of the image of scattering intensity. 
     
     
       5. The method according to  claim 1 , wherein the step of directing electromagnetic radiation into the edge surface of the polycrystalline semiconductor substrate comprises directing light of a laser beam into each edge surface. 
     
     
       6. The method according to  claim 5 , further comprising:
 detecting electromagnetic radiation of a first portion of one of the two opposite faces with the imaging optical detector and generating a first partial image therefrom; 
 detecting electromagnetic radiation of a second portion of the one of the two opposite faces with the imaging optical detector and generating a second partial image therefrom; and 
 composing a complete image from the two partial images. 
 
     
     
       7. The method according to  claim 5 , wherein at least one of the laser beams irradiates the polycrystalline semiconductor substrate at an oblique angle to an advance direction. 
     
     
       8. The method according to  claim 1 , further comprising performing at least one additional imaging selected from the group consisting of electro-luminescent imaging, photo-luminescent imaging, bright-field imaging, and dark-field imaging. 
     
     
       9. The method according to  claim 1 , wherein the step of placing the opaque structure between the face of the polycrystalline semiconductor substrate and the imaging optical detector comprises overlying the opaque structure on the face of the polycrystalline semiconductor. 
     
     
       10. The method according to  claim 1 , wherein the opaque structure comprises a busbar or a contact finger. 
     
     
       11. A method for detecting cracks in planar, polycrystalline semiconductor substrates that have two opposite faces and a circumferential edge surface, comprising:
 directing electromagnetic radiation into the edge surface of the polycrystalline semiconductor substrate, the electromagnetic radiation having a wavelength that is at least partially transmitted by the polycrystalline semiconductor substrate so that the electromagnetic radiation is directed from the edge surface for at least half a distance to a point opposite the edge surface by reflection at the two opposite faces, wherein the step of directing electromagnetic radiation into the edge surface of the polycrystalline semiconductor substrate comprises irradiating the polycrystalline semiconductor substrate with a light beam from a laser as a light source of the electromagnetic radiation, the light beam having a dimension that is larger than a thickness of the polycrystalline semiconductor substrate; 
 detecting electromagnetic radiation of at least a portion of one of the two opposite faces with an imaging optical detector that is sensitive to the electromagnetic radiation at the wavelength, wherein the electromagnetic radiation is scattered by the cracks and exits from one of the two opposite faces at sites of the cracks; 
 generating an image of scattering intensity from the electromagnetic radiation detected by the imaging optical detector; and 
 placing an opaque structure between the face of the polycrystalline semiconductor substrate and the imaging optical detector and recognizing a gleaming periphery of the opaque structure as a crack. 
 
     
     
       12. An apparatus for detecting cracks in planar, polycrystalline semiconductor substrates that have two opposite faces and a circumferential edge surface, comprising:
 a support for the polycrystalline semiconductor substrate; 
 a radiation source arranged in relationship to the support so that electromagnetic radiation from the radiation source is directed into the edge surface of the polycrystalline semiconductor substrate on the support, the electromagnetic radiation having a wavelength that is at least partially transmitted by the polycrystalline semiconductor substrate on the support; 
 an imaging optical detector sensitive to the electromagnetic radiation, the imaging optical detector being arranged in relationship to the support so that the imaging optical detector detects electromagnetic radiation that exits from one of the two opposite faces of the polycrystalline semiconductor substrate on the support; 
 an opaque structure between the face of the polycrystalline semiconductor substrate and the imaging optical detector; and 
 a computing device adapted to generate an image of scattering intensity of at least a portion of the face that is viewed by the imaging optical detector, the computing device being configured to recognize a gleaming periphery of the opaque structure as a crack. 
 
     
     
       13. The apparatus according to  claim 12 , wherein the radiation source comprises a laser, the apparatus further comprising:
 an advancing device configured to effect movement of the support and the laser relative to each other in a direction along the faces and transversely to the direction of incidence of the light, wherein the computing device is adapted to generate the image of scattering intensity during the relative movement. 
 
     
     
       14. The apparatus according to  claim 13 , wherein the laser is fixedly arranged in relation to the imaging optical detector and wherein the advancing device is adapted to move the support relative to the laser and the imaging optical detector. 
     
     
       15. The apparatus according to  claim 12 , wherein the imaging optical detector comprises one or more area array or linear array sensors. 
     
     
       16. The apparatus according to  claim 12 , wherein the radiation source generates two beams of electromagnetic radiation in opposite directions. 
     
     
       17. The apparatus according to  claim 16 , further comprising a trigger configured to intermittently clock the two beams, wherein the imaging optical detector is synchronized with the trigger so that the imaging optical detector intermittently generates detector signals of the scattered light from the two beams. 
     
     
       18. The apparatus according to  claim 16 , further comprising a trigger configured to intermittently clock the two beams separately from one another, wherein the imaging optical detector is synchronized with the trigger so that the imaging optical detector intermittently generates detector separate signals of the scattered light from each of the two beams. 
     
     
       19. The apparatus according to  claim 12 , wherein the radiation source generates a beam which illuminates at least one third of the width of the polycrystalline semiconductor substrate on the support. 
     
     
       20. The apparatus according to  claim 12 , wherein the radiation source is arranged to impinge light at an angle to the faces of the polycrystalline semiconductor substrate on the support.